svn commit: r289405 - head/sys/ufs/ffs

[Warner Losh]

> On Oct 16, 2015, at 2:12 AM, Hans Petter Selasky <hp at selasky.org> wrote:
> 
> On 10/16/15 08:21, Bruce Evans wrote:
>> In addition, making the file contiguous in LBA space doesn't
>>  improve the access times from flash devices because they have no seek
>> time.
> 
> Hi,
> 
> This is not exactly true, like Bruce pointed out too. Maybe there should be a check, that if the block is too small reallocate it, else leave it for the sake of the flash. Doing 1K accesses versus 64K accesses will typically show up in the performance benchmark regardless of how fast the underlying medium is.

But that’s not what this does. It isn’t the defrag code that takes the 2-8k fragments and squashes them into 16-64k block size for the device. This takes the larger blocks and makes sure they are next to each other. This takes large contiguous space (like 2MB) and puts as much as possible in a cylinder group. That’s totally useless on a flash drive.

Since the sizes of the blocks are so large, moving them won’t change any benchmarks.

Warner
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